NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Latitude by Lunar Distance
From: Frank Reed CT
Date: 2006 Sep 24, 06:33 -0500
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From: Frank Reed CT
Date: 2006 Sep 24, 06:33 -0500
That's no typo. Historically, lunar distances determine longitude, not
latitude. So why latitude?
Consider this scenario:
I am becalmed on the Grand Banks. I look up in the sky and see the
Moon close to due south about 45 degrees high, very roughly. The
horizon is obscured by fog; I cannot measure ordinary altitudes. Above the Moon,
I see Vega about 70 or 80 degrees high. I measure the angle between them with my
sextant as exactly as possible, recording the exact GMT. I do a little
math, and I have my latitude. Latitude by lunars?? Is such a thing
possible?! Sure, it's possible. By inverting the usual problem of lunar
distances, the measured distance yields the Moon's altitude, even when the
real horizon is quite invisible. Of course, it has fairly severe accuracy
limits... So how bad is it?? Could you determine your latitude by measuring a
lunar distance? Generally, could a certain class of lunar distance observations
be equivalent to ordinary altitude observations for lines of position? Can we
dispense with the horizon?
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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